In general, a metal foil (mainly a copper foil) is laminated on a polyimide film, a metal is deposited on a polyimide film by vapor deposition, plating, or sputtering, or a metal foil is coated with a polyimide precursor and then subjected to imidization by heating or the like to produce a single-sided copper-clad laminate. Furthermore, polyimide films of single-sided copper-clad laminates are bonded together with an adhesive to produce a double-sided copper-clad laminate which is further processed to a flexible printed wiring board. Namely, a polyimide film is used as a base film of a flexible printed wiring board. However, conventional polyimide films have the problem of low surface adhesiveness and thus cause defects in products without any processing. Therefore, polyimide films are surface-treated by corona discharge or plasma, for improving the surface adhesiveness. There is also a known method for roughening a surface of a polyimide film by adding inactive particles to a precursor or treating a film surface with a chemical.
Patent Document 1: Japanese Unexamined Patent Application Publication No. 8-143661.